The present invention relates to a ceramic filter arrangement having a plurality of effective surfaces for separating off entrained particles from a stream of molten metal.
Ceramic filters are known for purifying liquids. Ceramic filters have been successfully used in foundries, in order to keep impurities, such as slags, sand and refractory materials, away from the castings to be produced.
Ceramic filters having an open-cell foam structure are usually produced by impregnating an organic foam material, for instance polyurethane foam, with a low-viscosity ceramic slip or by impregnating the foam material with a high-viscosity slip and squeezing off the slip excesses by means of pairs of rollers.
WO 82/03339 discloses a ceramic filter of open-cell foam structure based on high-melting ceramic, which is produced by impregnating an organic foam material with a high-viscosity ceramic slip, drying, heating for removal of the foam material and calcining. Excess slip is removed after the impregnation of the foam material by passing the impregnated foam material through a system of pairs of rollers. Still further, exposed cell bridges located on the surface of the filter are secured against breaking off by additionally subjecting the dried impregnated foam material to a further impregnation with a ceramic slip on the surface. In this way, the temperature stability of the filter is enhanced. However, this further impregnation treatment is disadvantageous because not only the exposed cell bridges but also the filter regions located underneath are provided with the additional slip application. As a result, the permeability of the filter is impaired.
The fabrication of the ceramic filters described hereinabove, according to the state of the art, is very cost-intensive because of the diverse process sequences.